The present invention relates to a method for insulating glass windows, more particularly, to a method of filling the inner space of sealed insulating glass units with inert gas or mixture of gases.
Sealed insulating glass units typically consist of two parallel spaced apart lites of glass which are sealed along at their periphery such that the space between the lites, or the inner space, is completely enclosed. The inner space is typically filled with air. The transfer of energy through an insulating glass unit of this typical construction is reduced, due to the inclusion of the insulating layer of air in the inner space, as compared to a single lite of glass. The energy transfer may be further reduced by increasing the separation between the lites to increase the insulating blanket of air. There is a limit to the maximum separation beyond which convection within the air between the lites can increase energy transfer. The energy transfer may be further reduced by adding more layers of insulation in the form of additional inner spaces and enclosing glass lites. For example three parallel spaced apart lites of glass separated by two inner spaces and sealed at their periphery. In this manner the separation of the lites is kept below the maximum limit imposed by convection effects in the airspace, yet the overall energy transfer can be further reduced. If further reduction in energy transfer is desired then additional inner spaces can be added.
The energy transfer of sealed insulating glass units may be reduced by substituting the air in a sealed insulated glass window for a denser, lower conductivity gas. Suitable gases should be colorless, non-toxic, non-corrosive, non-flammable, unaffected by exposure to ultraviolet radiation, and denser than air, and of lower conductivity than air. Argon, krypton, xenon, and sulfur hexaflouride are examples of gases which are commonly substituted for air in insulating glass windows to reduce energy transfer.
A great variety of techniques have been developed for filling the inner space of insulating glass units with gas. Typically this is an exchange of gas, where the insulating glass unit originally contains air, present during the construction of the insulating glass units, which must be displaced or exchanged for the fill gas. It is desirable to achieve a high concentration of the fill gas in order to realize the maximum benefit of minimizing the energy transfer of the gas filled insulating glass unit. In practice the exchange of fill gas for air cannot be achieved without some mixing of the gases which results in a final concentration of the fill gas of less than 100%.
Several of the gas filling techniques make use of fact that all of the fill gases mentioned above are denser than air. One conventional technique involves the use of two probes. The first probe is used to feed the gas into the inner space and the second probe is used for exhausting air. The probes are inserted through bores provided in the sealing means at the periphery of the glass units. The bores in the sealing means must be sealed again after the gas exchange has been completed. The insulating glass unit is oriented such that the parallel spaced apart lites are vertical. The gas feeding probe is located at the bottom of the insulating glass unit and the exhausting probe is located near the top of the unit. This method is referred to here as the side filling method. The gas is introduced slowly into the inner space to minimize turbulent flow and to minimize mixing with the air in the inner space. The denser fill gas forces the less dense air towards the top of the airspace where it is exhausted at the exhaust probe. Some mixing with air will always occur and as such the volume of fill gas introduced is typically 1.75 to 2.00 times greater that the volume of the inner space. This over-filling is done in an attempt to also displace as much as possible of the fill gas air mixture such that a final concentration of greater than 90% fill gas is achieved.
In general a significant reduction in energy transfer may be realized for fill gas concentrations between 75% and 100%. However, the sealing means employed for insulating glass units typically have some low permeability which allows the fill gas to diffuse out of the inner space, due to the concentration gradient between the inner space and the ambient atmosphere, very slowly in service. To maintain the desired reduced level of energy transfer over the service life of the insulating glass unit the initial fill gas concentration is desired to be greater than 90% and is most desired to be greater than 95%. Depending on a number of factors associated with the overall design of the insulating glass unit and the edge sealing means the loss by diffusion of the fill gas may be limited such that the concentration of fill gas in the inner space may be maintained above 75% for 10-20 years or longer.
Another method, referred to here as the top filling method, involves orienting the insulating glass unit in the vertical position. Two bores are made in the top of the unit near opposite edges of the unit. A rigid or flexible tube for gas filling is inserted into the inner space and extends to the bottom of the unit along one side. The gas filling tube has multiple holes near the bottom of its length in order to minimize turbulent flow during filling. The tube is inserted into the inner space within two inches of the bottom of the unit. Fill gases, which are again denser than air, are charged through the tube to the bottom of the inner space. The fill gas displaces the air in a manner as described in the side filling method above. The volume of fill gas charged to the inner space is 1.75-2.00 times the volume of the inner space in order to also exhaust the volume of gas which has become partially mixed with air and achieve fill gas concentrations above 90%. The bores in the sealing means must be sealed again after the gas exchange has been completed.
The volume of fill gas to be charged in both of these methods may be calculated based on the size of the insulated glass units and adjusted for the amount of over-filling found through experience to give the typical desired final fill gas concentration. The fill volume is typically regulated by opening a valve in the fill gas supply line for a specified period of time while the gas is charged through a flow regulator set to a predetermined flow rate. Alternatively an oxygen analyzer may be attached to the exhaust port to monitor the oxygen content of the exhaust. The oxygen content is assumed to be proportional to the concentration of air in the mixture of fill gas and air in the exhaust from the inner space. The fill gas supply valve is turned off when the oxygen content in the exhaust falls below a level predetermined to provide the desired fill gas concentration. Using the oxygen analyzer means the size of the inner space to be filled need not be known and the volume of fill gas need not be calculated. Filling continues until the oxygen content, which is inversely proportional to the fill gas concentration, is less than the desired specification.
The maximum flow rate of fill gas into the insulated glass unit in both the side filling and the top filling methods is limited by 1) the desire to minimize turbulent flow, thereby minimizing mixing with the air in the unit; and by 2) the area of the of the exhaust bore or bores which will determine the back pressure within the inner space which if too high may damage the glass lites or the edge seal by forcing the glass lites apart. In general, for both the side filling and top filling method, a slow fill rate can achieve a high concentration of fill gas while limiting the amount of over-fill required. Faster filling rates can reduce the time required but will require higher over-fill rates to achieve the same final fill gas concentration. Even faster filling rates can cause so much turbulence and mixing of the fill gas with air in the inner space that desired fill gas concentrations cannot be achieved without using impractical over-filling amounts if at all.
Another method involves introducing a probe for gas exchange via an opening between the spacer frame and one of the glass units. This opening is produced by lifting and bending one glass lite at one comer so that it becomes partially separated from the edge sealing and spacing means. This is done by means of several suction cups attached to the lifted area while clamping other areas of the insulating glass unit. This means allows a high flow rate of fill gas as the opening for charging fill gas and exhausting the air can now be made large enough to mitigate pressure buildup. Air is withdrawn from the exhaust port. This technique is disadvantageous because there is an increased danger of breaking the stressed and displaced glass lite. A large amount of force is also necessary to lift the glass lite off the spacer frame. Due to the large opening shared by the charging and exhaust means a high level of over filling, 2.0 to 7.0 times the inner space volume, must be employed. This method lends itself to full automation of the filling process but does not significantly decrease the cycle time required.
These methods require more time to complete than the time required for the fabrication of the insulating glass unit prior to the gas filling step. Thus there must be an off line accumulation step to allow for gas filling in the production of insulating glass units. Multiple gas filling stations must be provided to allow filling of groups of units in order to maintain the desired overall production rate. Insulating glass units can be produced at a rate or cycle times between 20 to 60 seconds. Current rapid filling methods can achieve cycle times for the gas filling step of 40 to 120 seconds with significant over filling required to reach the desired fill gas concentration of greater than 90%. A faster gas filling method would overcome these problems to allow insulating glass units to be filled at the same rate as they are assembled. This would eliminate floor space, labor, and the need for multiple filling stations.
In accordance with the present invention, there is provided a method to efficiently and effectively fill the inner space of insulating glass units. The method comprises: positioning a glass unit, which has at least two sealingly connected outer walls spaced apart defining at least one inner space and at least one opening into the at least one inner space, at a selected position; charging a selected amount of at least one cryogenic liquid through the at least one opening into the at least one inner space of the glass unit; allowing the at least one cryogenic liquid to change into its gaseous state as it is warmed by the inner surfaces of the edge sealing means and glass at the bottom of the insulating glass unit, the increase in volume of the fill material as it changes from liquid to gas forces the air in the inner space above it out of the inner space; and sealing the at least one opening in the glass unit.
In the simplest embodiment of the present invention, the cryogenic liquid is suitably poured manually into the inner space using an insulated container and a funnel to direct the liquid through a small hole in the edge sealing means of the insulating glass unit. The desired amount of liquid is suitably pre-measured volumetrically. The liquid is allowed to boil and/or evaporate in the inner space forcing the lighter air out, and the opening is sealed.
In a preferred embodiment of the present invention, the cryogenic liquid is dispensed into the inner space by a specially designed cryogenic liquid dosing machine. The machine has volumetric sensing aspects which sense the length and width of the glass units and the separation of the outer walls defining the inner space. The dosing machine calculates the amount of cryogenic liquid required.
The method of filling the inner space of insulating glass units with cryogenic liquid allows the insulating glass units to be filled more quickly, thus cycle times customary for insulating glass manufacture can be maintained. Additionally, even windows containing grids between the window panes can be filled more quickly. In conventional gas fill methods, the grids tend to cause more turbulence during the gas fill process. Whereas, the method of the present invention allows for accelerated gas fill without these turbulent effects. Overall, the method accelerates the gas-filling process and reduces the waste and turbulent effects normally associated with the quickest conventional gas-fill methods.
These and other aspects of the invention are herein described with reference to the accompanying Figures which are representative of various embodiments in which the principles and concepts of the invention can be embodied.